How many sea turtles did we lose from oil spill?

One of the world’s the largest oil-spill disaster happened while oil wells were being drilled in the Gulf of Mexico on April 20, 2010. About 210 million gallons of oil were discharged into the ocean and harmed vegetation, wildlife, and the economy of the area. During the 6 months after the accident, among 1,066 sea turtles collected, only 520 were found alive.

How many sea turtles were found dead?

Which number was larger, sea turtles found alive or sea turtles found dead? And what was the difference in the two numbers?